More worrying for him is what I would have done , I've always had an explosive temper and martial arts hasn't really mellowed that temper all that much .
Its just enabled me to take it out on the heavy bag with more finesse and power than I would of been able to previously.
Hey, I thought I was the one with the temper and your the mellow one! lol!
I did stuff like that to Hubbie when I first started. Not as mean, I didn't really try to break his fingers or anything, but I wanted to see if wing chun could counter and defend against my awesome ju-jitsu. lol!
I could never even get a hold on him long enough to flex a joint. Really impressed the heck out of me.
I didn't do this in class, mind you. We did some private lessons too and that's usually when I'd play around more, I didn't want to do anything like that in front of other students.
But, having a background in TSD, karate, really made it difficult for me to literally move forward in WC when I first started. Everytime he'd punch at me I'd bob my head and step to the side or step back. I just couldn't help it most of time. My body just wouldn't step forward into the punch. Years of training to "dodge" the punch, block and back or side step. Very aggravating.
I see students that have never taken an art and they just pick up all the basics on a level of ease that I wish I'd had.

I had to drill everything double time to get that damn muscle memory out. I still do!
Now that we're working on the neck throws and the closer range of WC/WT my JJJ really jacks me up. When were torso to torso, hip to hip, that close my JJJ wants to kick in and grab, throw, sweep, choke. And doing application where you react off his movement there isn't alot of time to think, just act. This is when I always wonder, what will come out JJJ or wing chun? ack! frustrating!
As for power generation in an experienced MA student in reguards to a student without MA experience. This is what I've noticed..
A previously trained MA will punch the bag harder than the unexperenced student, sure. But their energy is wrong for wing chun. Their power is all force and external more often than not, so in a way, their force is an illusion. The new student with the "weaker" punching will learn to generate more internal power sooner, sometimes those from other arts just never really fully grasp the power of WC punching and striking.
A TKD background is even worse for the WC kicking. I've had a hard time teaching hook kick to TKD guys because they just can't get that TKD roundhouse knee "pop" out of the kick. Not to mention getting them to stop the corkscrew punching.
I do think some people can just adapt from one martial art to another. I used to think I was one of those people. I hopped from TSD, to JJJ, to kali, to Wu Wei kung fu, go ju ryu, Tai Chi, etc with no dificulty at all. (except tai chi, I was an impatient 18 year old! I'm an impatient 32 year old! lol!)
I could transfer from one to the other in the very same day! (I actually got to train with Shodai for a year and took a different style every hour for 5 hours a day. Those were the coolest days for an 18 year old punk rock girl! lol)
But, when I got fully into WC I just couldn't pick up the technques as fast as I'd had in other arts. It was weird. I'd always picked techniques up really fast in other arts, easy. But, not Wing Chun, I actually had to work hard at it. lol! And I'd come to find that nothing I'd trained before was of any help whatsoever in my new wing chun training.
But, aparently others have had an eaiser time of it than me.

This is the first art I've ever taken that hasn't just come easy to me. And it was a big hit home when I first took it. I knew then that this was the one art for me, that I didn't need another. And I'd never felt like that with any art. Alot does come very naturally to me, but the closer I get in the more I struggle against prior training habits, and the more hesitation and less flow.